This invention relates generally to air pumps and more particularly to a carbon vane dry air pump. Commonly available dry vacuum pumps comprise mechanical carbon rotors and vanes operating in a hardened metal ellipsoidal cavity. These pumps provide a power source for, among other things, gyroscopically controlled, pneumatically operated flight instruments.
A dry air type rotary vane pump usually has a rotor with radial slots, vanes that reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their rotor slots. The reciprocating vanes thus extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine.
Because dry air pumps do not use a liquid lubricant, forms of dry lubrication have been developed. For example, vanes for rotary pumps have been manufactured from carbon or carbon graphite. These parts rub against other stationary or moving parts of the pump during operation. Graphite dust from these parts is deposited on the opposing parts by the rubbing action and forms a low friction film between the parts, thereby providing lubrication. The deposited graphite film is itself worn away by continued operation of the pump, and is eventually exhausted out of the pump. The film is replaced by further wear of the carbon graphite parts. Thus, lubrication is provided on a continuous basis that continuously wears away the carbon graphite parts.
One of the primary causes of carbon vane dry pump failure is contamination with engine lubricating oil. If engine lubricating oil passes through the drive system into the interior of the pump in moderate quantities, it will mix with the graphite dust to form a viscous sludge which has poor lubricating properties. This causes overheating and eventual seizing and failure. Because the seals used at the air-oil interface of commercially available pumps and drives are not 100% effective, drain openings are usually provided for draining any leaking oil before it reaches the carbon vanes. However, the drain openings used in the prior art require that a significant portion of the pump housing fill with oil before it drains. This causes the shaft to pick up and sling the oil through drain openings in several directions from the pump. This makes it difficult to determine the source of an oil leak. Furthermore, this drain arrangement collects a significant quantity of oil at the air-oil interface which increases the probability that the oil will migrate into the vane chamber. Finally, because the drains are usually arrayed all the way around the pump to create a “universal” fit air pump, the drive area is open and can be easily contaminated, for example during an engine solvent wash.
Accordingly, it is an object of the invention to provide a vane pump which resists leakage of oil into the working parts of the pump.
It is another object of the invention to provide a vane pump which provides an easily interpreted indicator of the source of a lubricating oil leak.
It is another object of the invention to provide a universal-fit air pump having an air seal which is easily installed in a correct position.
It is another object of the invention to provide a vane pump which provides improved sealing between its component parts
It is another object of the invention to provide a vane pump having the shortest possible leakage path.